The Extensible Markup Language (XML) is a standard for encoding textual information that has been recommended by the World Wide Web Consortium (W3C). For a discussion of the XML standard, see, for example “Extensible Markup Language (XML) 1.0 W3C Recommendation”, incorporated by reference herein. The XML standard allows XML-enabled applications to inter-operate with other compliant system for the exchange of encoded information.
XML documents store textual data in a hierarchical tree structure. Each XML document has one root node, often referred to as the root element, with the other nodes in the hierarchical tree being arranged as descendants of the root node. The XML standard specifies four types of nodes, namely, character nodes, processing instruction (PI) nodes, comment nodes and element nodes. A character node contains only one character. A processing instruction node contains a name field and a content field (a sequence of characters). A comment node has only a content filed (a sequence of characters). Character nodes, processing instruction (PI) nodes and comment nodes are always leaf nodes in an XML document. Element nodes have children, a name (often referred to as a generic identifier (GI)), and a set of attributes (keyword-value pairs). An XML-based application can store data in all the different types of nodes and in all the fields of each node type.
A number of applications, such as video on demand and other continuous media applications, have emerged for encoding and transmitting continuous media streams. The proposed MPEG-7 standard, for example, from the Motion Pictures Group, provides a specification for encoding video information as well as textual information related to the video source. Continuous media streams are typically transmitted using a packet-based communication system. Due to the unreliable nature of packet-based communication systems, however, the quality of the received stream may be impacted by packet loss. Thus, such continuous media transmission systems generally must include a mechanism that allows the receiver to adapt to lost packets. A number of techniques have been proposed or suggested for addressing packet loss in a continuous media transmission system, including redundant transmissions, retransmission, interleaving and forward error correction techniques. For a general discussion of such techniques for addressing packet loss in continuous media systems, see, for example, “Options for Repair of Streaming Media,” Network Working Group, Request for Comments No. 2354 (June 1998), incorporated by reference herein.
XMLNet is an application programming interface (API) for streaming XML documents. XMLNet allows information to be transferred over the Internet or another network in real time as a series of XML documents. The XML documents are delivered to the receiver in a serial fashion. The receiver must receive an entire XML document, however, before the receiver can decode and process any of the XML content contained in the XML document. For a discussion of XMLNet, see for example “XMLNet,” Dec. 9, 1998 downloadable from.
A need therefore exists for a method and apparatus that allows a receiver to decode the portions of the XML encoded content that are actually received, even if portions of the complete XML document are not received, for example, in the event of a packet loss or before the complete XML document is received. A further need exists for a method and apparatus that permits streaming of XML content in a manner that allows the transmitted XML to be decoded by the receiver even if an entire XML document is not received.